A compact and robust laser configuration was achieved by using an all-fiber configuration with single mode fibers and fiber Bragg gratings (FBG). Different FBG pairs with wavelength around 2 μm were tested. To achieve stable polarized output power the fibers with the FBG were 90° twisted at the splices. Stable linearly polarized output power up to 38 W with an extinction ratio of up to 50:1 was observed. With respect to the diode output power an optical-to-optical efficiency of 51 % was reached with a correspondent slope efficiency of 52 %. The emission linewidth at maximum power was measured to be < 0.3 nm which is well suitable for Ho-laser pumping. First tests of the precise processing of highly transparent plastic materials demonstrate the potentials of these laser systems.
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K. Scholle, M. Schäfer, S. Lamrini, M. Wysmolek, M. Steinke, J. Neumann, P. Fuhrberg, "All-fiber linearly polarized high power 2-µm single mode Tm-fiber laser for plastic processing and Ho-laser pumping applications," Proc. SPIE 10512, Fiber Lasers XV: Technology and Systems, 105120O (26 February 2018);